Full report of nuclear test fallout released
(This story appeared on page 231 of the
Oct. 11, 1997, Science News.)
By Sid Perkins
Science News
Everybody got a little, but some got quite a bit - possibly more than was
good for them.
On Oct. 1, the National Cancer Institute released the full report on its
nationwide study of exposure to atmospheric fallout from 90 above-ground
nuclear tests conducted 65 miles northwest of Las Vegas throughout the
1950s and 1960s. Wind and rain deposited the fallout from each of the
tests in different areas.
Faye Austin, director of NCI's division of cancer biology in Rockville,
Md., says the report shows that everyone in the continental United States
was exposed to radioactive iodine-131 for about 2 months following each of
the tests. The amount of exposure depended on where the people lived and
what they ate. Because I-131 accumulates in the thyroid gland, doctors
have raised concerns that fallout might pose a threat of thyroid cancer
to people exposed to it as children.
Exposure to I-131 came about mainly through drinking milk from cows
or goats that had eaten fallout-tainted vegetation. Smaller exposures
arose from breathing contaminated air or eating other foods, such as eggs
and leafy vegetables, Austin says.
People who drank milk from backyard cows probably received higher doses of
radiation than those who drank commercially processed milk. Unprocessed
milk was likely to have been consumed more quickly after milking, and half
of the radioactivity associated with I-131 disappears every 8
days.
Although NCI's report is the first widely-known account of exposure,
federal officials suspected as early as 1953 that I-131 could show up in
milk products, say Pat Ortmeyer and Arjun Makhijani of the Institute for
Energy and Environmental Research in Takoma Park, Md. Ortmeyer says the
officials also knew details of fallout patterns. After Eastman Kodak Co.
in Rochester, N.Y., complained to the government in 1951 about
radiation-fogged film, the Atomic Energy Commission agreed to provide
routine fallout predictions and follow-up information to several film
manufacturers.
Ortmeyer and Makhijani found no evidence that the government informed the
dairy industry or the public, they report in an article scheduled for
publication in the November-December BULLETIN OF THE ATOMIC
SCIENTISTS.
For each nuclear test and for every county in the lower 48 states, NCI
researchers used fallout measurements and weather data from the time of
the tests to estimate average I-131 doses for people in 13 age groups,
including fetuses. They then estimated average doses for 4 subgroups,
categorized by their milk-drinking habits, within each age group.
The highest average amounts of radiation absorbed by thyroid tissue, in
the range of 5 to 16 rads, occurred in parts of Utah, Idaho, Montana,
Colorado, and Missouri. In contrast, a routine 1950s test for
thyroid abnormality in children, which used I-131, delivered a dose
of about 200 to 300 rads.
Limited data from a previous study of Utah "downwinders" provided
"suggestive, but not conclusive" evidence that childhood exposure to I-131
is linked to thyroid cancer, Austin says. The NCI study does not address
the question of cancer risk directly, she cautions.
The National Academy of Science's Institute of Medicine plans to convene a
panel to review the full NCI report, as well as other studies, to see if
the health risks from exposure to fallout can be quantified. The panel
will also seek to develop guidelines for physicians on how to identify
persons who might be at increased risk for thyroid cancer, Austin
says.
In a separate analysis, NCI also looked at seven previous studies of
people exposed to external radiation from sources as diverse as treatment
for disease and the atomic bombings of Hiroshima and Nagasaki. These data
show that, on average, persons exposed as young children to 100 rads of
external radiation had a 8.7 times the risk of developing thyroid cancer
as nonexposed children.
Each year, about 16,000 U.S. residents are diagnosed with thyroid cancer,
and an estimated 1,230 die. The disease, often curable, accounts for just
under 1 percent of all cancers in the United States.
Researchers at NCI estimate that the nuclear fallout from the Nevada Test
Site may ultimately cause between 7,500 and 75,000 cases of thyroid
cancer, an increase of 2 to 20 percent above the normal number.
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Copyright 1997 by Science Service.
All rights reserved.
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